Copper post-etch cleaning process

ABSTRACT

The invention includes a method of cleaning a surface of a copper-containing material by exposing the surface to an acidic mixture comprising NO 3   − , F −  and one or more organic acid anions having carboxylate groups. The invention also includes a semiconductor processing method of forming an opening to a copper-containing material. A mass is formed over a copper-containing material within an opening in a substrate. The mass contains at least one of an oxide barrier material and a dielectric material. A second opening is etched through the mass into the copper-containing material to form a base surface of the copper-containing material that is at least partially covered by particles comprising at least one of a copper oxide, a silicon oxide or a copper fluoride. The base surface is cleaned with a solution comprising nitric acid, hydrofluoric acid and one or more organic acids to remove at least some of the particles.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/083,035 which was filed on Oct. 24, 2001 now U.S. Pat No. 6,589,882and which is incorporated by reference herein.

TECHNICAL FIELD

The invention pertains to methods of cleaning surfaces ofcopper-containing materials. In particular embodiments, the inventionpertains to semiconductor processing methods of forming openings tocopper-containing substrates.

BACKGROUND OF THE INVENTION

Copper has a relatively high conductance compared to many otherelements, and accordingly can be desired for utilization as a wiringlayer in various circuitry applications. For instance, in semiconductorprocessing applications, it can be desired to provide copper wiringlayers as electrical paths to various integrated circuit components.

A difficulty in utilizing copper in semiconductor processingapplications is that it can be difficult to clean. For instance,copper-containing materials will frequently have a surface to whichelectrical connection with other conductive components is ultimately tooccur. Formation of such electrical connection will frequently involveproviding a conductive material over the surface of thecopper-containing material. The conductive material is intended tophysically contact the surface of the copper-containing material to forman electrical connection with the copper-containing material. However,if the surface of the copper-containing material is partially orentirely covered with debris, the physical connection of the conductivematerial and copper surface can be impaired. Such impairment can lead toattenuation of electrical current passing between the copper-containinglayer and the conductive material formed thereover.

It would be desirable to develop improved methods of cleaningcopper-containing surfaces to remove debris from over the surfaces priorto forming conductive materials thereon.

SUMMARY OF THE INVENTION

In one aspect, the invention encompasses a semiconductor processingmethod of cleaning a surface of a copper-containing material by exposingthe surface to a mixture having an acidic pH and comprising NO₃ ⁻, F⁻and one or more organic acid anions, where at least some of the organicacid anions contain carboxylate groups.

In another aspect, the invention includes a semiconductor processingmethod of forming an opening to a copper-containing material within asubstrate. The substrate contains a semiconductor material and has afirst opening. A copper-containing material is provided within the firstopening and a mass is formed over the substrate and over thecopper-containing material. The mass comprises at least one of an oxidebarrier material and a dielectric material. A second opening is etchedthrough the mass into the copper-containing material. A surface of thecopper-containing material defines a base of the second opening and isreferred to as a base surface. The base surface of the copper-containingsubstrate is at least partially covered by at least one of a copperoxide, a silicon oxide or a copper fluoride. The base surface is cleanedwith a cleaning solution having an acidic pH and comprising nitric acid,hydrofluoric acid and one or more organic acids. At least some of theorganic acids have one or more carboxylic acid groups. The cleaningremoves at least some of the at least one of a copper oxide, a siliconoxide and a copper fluoride from the base surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic, fragmentary, cross-sectional view of asemiconductor wafer fragment at a preliminary step of a processingmethod of the present invention.

FIG. 2 is a view of the FIG. 1 wafer fragment shown in a processing stepsubsequent to that of FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer fragment shown in a processing stepsubsequent to that of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theConstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The invention encompasses utilization of a mixture comprising NO₃ ⁻, F⁻and one or more organic acid anions, where at least some of the organicacid anions comprise one or more carboxylate groups, for cleaningsurfaces of copper-containing materials. A wide range of organic acidsthat comprise carboxylic acid groups may be utilized for purposes of thepresent invention. Examples of such acids include, but are not limitedto, formic acid, acetic acid and CH₃(CH₂)_(x)CO₂ ⁻, where x is less thanor equal to 3. In the discussion examples that follow acetic acid isused as an exemplary acid for purposes of explaining the presentinvention. It is to be understood, however, that the present invention,encompasses numerous alternative organic acids.

The mixture for cleaning surfaces of copper-containing materials can beformed by, for example, combining an acetic acid solution (which can beobtained as, for example, a 99.8% (by weight) solution), an HF solution(which can be obtained as, for example, a 49% (by weight) solution of HFin water), an HNO₃ solution (which can be obtained as, for example, a70.4% (by weight) solution of HNO₃ in water) and H₂O. The pH of themixture is acidic and preferably is less than about 6, more preferablyfrom about 1 to about 4, and yet more preferably from about 1 to about2.

If the one or more organic acids used in the cleaning solution comprisesacetic acid, the relative amounts of acids contained in the finalsolution used for cleaning can be, for example, from about 3% to about20% acetic acid by weight, from about 0.1% to about 2% HNO₃ by weight,and from about 0.05% to about 3.0% HF by weight.

The cleaning solution can be utilized without adjustment of theresulting pH after mixing water and acid solutions. Alternatively, abase can be added to the mixture to adjust the mixture to a desired pHwithin the acidic range. An exemplary base for purposes of the pHadjustment is NH₄OH, although other bases can be used alternatively orin addition to NH₄OH.

Although the above-described process forms a mixture comprising a basecation in combination with the acetate anion, NO₃ ⁻ and F⁻ by adding abase to an acidic mixture of HF, acetic acid, and HNO₃, it is to beunderstood that identical mixtures can be formed by combining varioussalts in an aqueous solution. For instance, if a base cation is NH₄ ⁺, amixture of the base cation with the acetate anion, NO₃ ⁻, and F⁻ can beformed by combining NH₄F with ammonium acetate and NH₄NO₃.Alternatively, the mixture can be formed by combining one or moreammonium salts selected from the group consisting of NH₄F, NH₄NO₃, andammonium acetate with one or more acid selected from the groupconsisting of acetic acid, HF and HNO₃.

The mixtures formed by the above described combination of acid solutionwhere the pH of the solution is not adjusted, will preferably consistessentially of NO₃ ⁻, F⁻, and the acetate anion, together withequilibrium components of H₃O⁺ and H₂O. The equilibrium components ofH₃O⁺ and H₂O will be understood by persons of ordinary skill in the artto comprise chemicals in equilibrium with H₃O⁺ and H₂O, such as forexample, OH⁻ (i.e., the hydroxide anion). Another way of describing amixture of the present invention is as an aqueous mixture comprisingnon-aqueous anions consisting essentially of the acetate anion, NO₃ ⁻and F⁻, or, in particular embodiments, comprising non-aqueous anionsconsisting of the acetate anion, NO₃ ⁻ and F⁻. Such descriptionconsiders the equilibrium components of H₃O⁺, OH⁻ and H₂O to be aqueouscomponents of the mixture. Yet another way of describing a mixture ofthe, present invention is that such mixture is a solution in which theonly non-hydroxide anions consist essentially of the acetate anion, NO₃⁻ and F⁻, or in particular embodiments, consist of the acetate anion,NO₃ ⁻ and F⁻.

An advantage of using a solution comprising acetate, NO₃ ⁻ and F⁻ forcleaning copper in semiconductor fabrication processes is that suchsolution can remove a variety of common contaminants in a singleprocessing step. For instance, HF or F⁻ can remove silicon oxides (forexample, SiO₂), as well as copper oxides; and HNO₃ or NO₃ ⁻ can removeelemental copper. The solution of the present invention can also removecopper oxides (such as for example, Cu₂O and CuO), and copper fluorides(CuF and CuF₂).

In addition, it is advantageous for the solution to comprise an organicacid comprising one or more carboxylic acid groups, for instance, aceticacid, rather than an inorganic acid such as, for instance, HCl, becausethe cleaning solution comprising the organic acid can be more selectivefor contaminating particles such as copper oxides, silicon oxides andelemental copper, relative to various semiconductor structuralcomponents than could the corresponding cleaning solution where theorganic acid is replaced with, for example, HCl. For this reason, thecleaning solution of the present invention that comprises an organicacid rather than HCl is more compatible with structural components suchas: aluminum nitride; a composition comprising silicon, carbon andhydrogen; copper; low-k dielectric materials, and organic materials. Thecleaning solution of the present invention comprising organic acid canalso be more selective relative to aluminum oxide than the correspondingcleaning solution comprising HCl. Therefore, if aluminum oxide is astructural element, the cleaning solution of the present invention willbe less likely to etch the aluminum oxide element during the cleaningthan a corresponding hydrochloric acid cleaning solution.

A semiconductor processing method incorporating a copper cleaningprocedure encompassed by the present invention is described withreference to FIGS. 1-3.

Referring first to FIG. 1, a semiconductive material wafer fragment 10is illustrated at a preliminary processing step. Wafer fragment 10comprises a semiconductive material substrate 12 having a first opening14 therein. A copper-containing material 22 is formed within firstopening 14. Substrate 12 can comprise, for example, a monocrystallinesilicon wafer having various levels of circuitry formed there over. Toaid in interpretation of the claims that follow, the terms“semiconductive substrate” and “semiconductor substrate” are defined tomean any construction comprising semiconductive material, including, butnot limited to, bulk semiconductive materials such as a semiconductivewafer (either alone or in assemblies comprising other materialsthereon), and semiconductive material layers (either alone or inassemblies comprising other materials). The term “substrate” refers toany supporting structure, including, but not limited to, thesemiconductive substrates described above.

Copper-containing material 22 can comprise, for example, a copper alloy,a copper compound, or elemental copper, and can be formed by, forexample, sputter deposition. In particular embodiments,copper-containing material 22 will consist essentially of elementalcopper (or consist of elemental copper) and will define a wiring layerfor connecting various circuitry components (not shown) associated withfragment 10.

In addition to the features described above, semiconductive materialwafer fragment 10 can comprise a copper-barrier material 20. As shown inFIG. 1, copper-barrier material 20 can form a layer within first opening14, and can be over the surface 18 and the sidewalls 16 of the opening.Copper-containing material 22 can be formed over copper-barrier material20. Copper-barrier material 20 can comprise, for instance, one or moreof Ta, TaN, Ti, TiN, and W. In particular embodiments, copper-barriermaterial could consist essentially of, one or more of Ta, TaN, Ti, TiN,and W.

Referring to FIG. 2, a mass 24 is formed over substrate 12 and overcopper-containing material 22. Mass 24 comprises at least one of anoxide barrier material (for example, Al₂O₃, SiO₂, SiC, siliconoxynitride or a composition comprising silicon, carbon and hydrogen) anda dielectric material (for example, SiO₂, SiO, and low-k dielectricmaterials such as: SILK™, Dow Chemical Corp.; BLACK DIAMOND™, AppliedMaterials; and CORAL™, Novellus). The shown mass 24 comprises two layers26 and 28 which are formed one atop the other. One of the layers 26 and28 can comprise an oxide barrier material and the other of the layerscan comprise a dielectric material. For instance, layer 26 could consistessentially of Al₂O₃, SiO₂, silicon oxynitride, or a compositioncomprising silicon, carbon, and hydrogen (or in particular embodiments,layer 26 could consist of Al₂O₃, SiO₂ or silicon oxynitride) and layer28 could consist essentially of SiO₂, low-k dielectric materials (seeabove), and SiO, (or in particular embodiments, layer 28 could consistof SiO₂, low-k dielectric material, or SiO). Such layers 26 and 28 canbe formed by, for example, chemical vapor deposition.

In addition to the above described features, mass 24 can comprise alayer of barrier material 30 over copper-containing material 22. Asshown, layer 30 can be between copper-containing material 22 and layers26 and 28 of mass 24. Barrier material 30 can comprise, for instance oneor more of a bottom anti-reflective coat material (BARC), a dielectricanti-reflective coat material (DARC), aluminum nitride, or siliconcarbide materials such as BLOK™ (Applied Materials). Layer 30 can beformed, for instance, by chemical vapor deposition.

Still referring to FIG. 2, a second opening 32 is etched through mass24, and specifically is etched through both layers 26 and 28. Inembodiments having layer 30, opening 32 can be formed by an open barrieretch process that etches through layer 30 to expose copper-containingmaterial 22, as shown. In alternate embodiments, a closed etch processmay be utilized to form opening 32. A closed etch can allow at leastsome thickness of layer 30 to remain over copper-containing material 22such that copper-containing material is not exposed (not shown). Opening32 can be formed by, for example, photolithographic processing wherein aphotoresist masking layer (not shown) is formed over mass 24 andpatterned to protect some of mass 24 while leaving a portion of mass 24exposed to etching conditions which ultimately form opening 32.

In embodiments that comprise an open etch, opening 32 can extend to anupper surface 34 of copper-containing material 22. Surface 34 defines abase of opening 32, and the portion of surface 34 within opening 32 canbe referred to as a base surface.

Base surface 34 is partially covered by contaminating particles 36. Suchcontaminating particles can comprise, for example, one or more of acopper oxide, a silicon oxide, a copper fluoride, or a carbon containingresidue such as carbon-fluoride polymers. Additionally, particles 36 cancomprise elemental copper left over from a sputter deposition ofcopper-containing material 22. The copper oxide, silicon oxide, copperfluoride, or carbon-fluoride polymer particles can be formed, forexample, during the etch through layers 26 and 28. For instance, thesilicon oxide can be formed by either oxidation of a silicon nitridecomponent of mass 24, or by debris occurring during the etch of asilicon oxide component of mass 24. As another example, copper oxide canbe formed from portions of copper-containing material 22 exposed toetching conditions, if such conditions comprise oxidative components. Asyet another example, copper fluoride can be formed from portions ofcopper-containing material 22 exposed to etching conditions if suchconditions comprise a fluorine-containing etchant such as, for example,CF₄.

Although base surface 34 is shown to be only partially covered bycontaminating particles 36, it is to be understood that such particlescan entirely cover base surface 34. The particles 36 can also bedeposited on the sidewalls of opening 32 and on the surface of 28.

Although the contaminating particles 36 are described as being formedduring formation of opening 32, it is to be understood that particles 36could be formed during other processing steps, such as for example, asresiduals from a chemical mechanical polishing process step.

Referring to FIG. 3, contaminating particles 36 (FIG. 2) are removedfrom base surface 34 by cleaning such surface with a mixture of thepresent invention comprising NO₃ ⁻, F⁻, and one or more organic acidanions, wherein the organic acid anions comprise one or more carboxylategroups, such as a composition with an acidic pH and comprising NO₃ ⁻,F⁻, and the acetate anion. More specifically, base surface 34 is cleanedby exposing the surface to the mixture of the present invention which isdescribed above for removing copper oxide, silicon oxide, copperfluoride, and elemental copper from over base surface 34 in one cleaningstep. Such cleaning solution preferably is an aqueous mixture comprisingionic components, with the ionic components consisting essentially ofF⁻, NO₃−, and one or more organic acid anions having one or morecarboxylate groups. Such organic acid anions can be for example formate,acetate, or CH₃(CH₂)_(x)CO₂ ⁻, where x is less than or equal to 3. Thecleaning mixture can have such preferred composition at least until basesurface 34 is exposed to the mixture. Once base surface 34 is exposed tothe mixture, a composition of the mixture can change to includecomponents released from particles 36 (FIG. 2) during the removal ofparticles 36 from over base surface 34 with the mixture.

The exposure of base surface 34 to the mixture comprising NO₃−, F⁻, andone or more organic acid anions can occur for a time from about 10seconds to about 1 hour at a temperature from about 10° C. to about 40°C., and at atmospheric pressure. The temperature can comprise, forexample, ambient temperature (typically from 20° C. to 30° C.). Suchexposure to the mixture can comprise, for example, immersion,submersion, spray-rinsing, brush-scrubbing, spin-processing, agitation,recirculation, spray-application, the use of megasonics, or acombination of any of these techniques.

Relative amounts of F⁻, NO₃ ⁻ and organic acid anions within a cleaningmixture of the present invention can be varied depending upon particularcleaning conditions. For instance, if a large amount of silicon oxidecontamination is expected to be present, the concentration of F⁻ can beincreased relative to the concentrations of NO₃ ⁻ and organic acidanions. On the other hand, if elemental copper is particularlyproblematic, the concentration of NO₃ ⁻ can be increased relative to theconcentrations of F⁻ and organic acid anions. Further, if copper oxidesare particularly problematic, the concentration of organic acid anionscan be increased relative to the concentrations of NO₃ ⁻ and F⁻. Also,it can be desirable to increase the total concentration of organic acidanions, NO₃ ⁻ and F⁻ to accomplish faster cleaning of acopper-containing substrate. Faster cleaning can also be accomplished byincreasing a temperature of the cleaning solution and/or a temperatureof the copper-containing material during a cleaning process.

Relative concentrations of NO₃ ⁻, F⁻ and organic acid anions can also bevaried to avoid having one or more of the various anions etching noncontaminating portions of wafer fragment 10. For instance, a method ofexposing base surface 34 to a cleaning solution of the present inventionis to dip a wafer comprising fragment 10 into a cleaning solution of thepresent invention for a time of about 5 minutes. Such dip would exposelayers 26 and 28 to the cleaning solution, as well as exposing basesurface 34 to the cleaning solution. If one or both of layers 26 and 28comprise silicon dioxide, the silicon dioxide would be expected to beetched by F⁻ present in the cleaning solution. Such etching could altera configuration of layers 26 and 28 if the concentration of F⁻ wheresufficiently high, or if the time of exposure where sufficiently long.For instance, if an interface 27 is defined at a location where layers26 and 28 join, and if it is considered that one of layers 26 and 28comprises silicon nitride and the other comprises silicon dioxide, thenthe exposure to F⁻ in the cleaning solution may form divit at locations29 where interface 27 is exposed along sidewalls of opening 32. A methodof avoiding such divit formation is to adjust a concentration of F⁻within the cleaning solution that the F⁻ concentration is only enough toremove contaminating particles 36 from base surface 34. In other words,to adjust the concentration of F⁻ within the cleaning solution so thatthere is enough F⁻ to remove particles 36, but not enough todetrimentally affect exposed silicon oxide surfaces of mass 24 duringthe time of exposure to the cleaning solution.

Preferably, if a silicon oxide containing surface of mass 24 is exposedto a cleaning solution of the present invention during a cleaning ofbase surface 34, the concentration of F⁻ within the mixture will be suchthat less than 5 angstroms of silicon oxide is removed from the exposedsurface of mass 24 during the cleaning of the base surface.

In addition to the features described above, the present invention canbe used to clean contaminants from surfaces resulting from a closedbarrier etch (described above) that does not expose copper-containingmaterial 22. The cleaning solution and methods described can be utilizedto remove post-closed barrier etch contaminants from the surfaces ofopening 32, including surfaces comprising barrier material 30. Suchcleaning can be performed without substantially degrading material layer30 or other exposed surfaces of opening 32 (discussed above).

It is to be understood that the present invention contemplatesadaptation for use cleaning semiconductor surfaces other than copper.Such adaptation includes adaptation for both metallic and non-metallicsurfaces.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A semiconductor processing method of forming anopening to a copper-containing material within a substrate, comprising:providing a substrate comprising a semiconductive material; forming afirst opening within the semiconductive material; after forming theopening, depositing a copper-containing material within the firstopening; providing a mass over the substrate and over thecopper-containing material, the mass comprising at least one of an oxidebarrier material and a dielectric material; etching a second openingthrough the mass and to the copper-containing material, a surface of thecopper-containing material forming a base of the second opening and thusdefining a base surface of the second opening, said base surface beingat least partially covered by at least one of a copper oxide, a siliconoxide and a copper fluoride; and cleaning the base surface with amixture comprising, NO₃ ⁻, F⁻ and one or more organic acid anions toremove at least some of the at least one of a copper oxide, a siliconoxide and a copper fluoride from the base surface; wherein at least someof the organic acid anions comprise one or more carboxylate groups, andwherein the mixture has a pH of less than about
 6. 2. The method ofclaim 1 wherein the copper-containing material consists essentially ofelemental copper.
 3. The method of claim 1 wherein the first openingcomprises sidewalls and a surface the method further comprisingdepositing a copper-barrier layer within the first opening and over thesidewalls and surface of the opening, and wherein the providing thecopper-containing material comprises providing the copper-containingmaterial over the copper-barrier layer.
 4. The method of claim 3 whereinthe copper-barrier material comprises one or more members selected fromthe group consisting of Ta, TaN, Ti, TiN, and W.
 5. The method of claim1 wherein the oxide barrier material comprises one or more materialsselected from the group consisting of Al₂O₃, SiO₂, aluminum nitride,silicon oxynitride, silicon carbide, and a composition comprisingsilicon, carbon and hydrogen.
 6. The method of claim 1 wherein thedielectric material comprises one or more materials selected from thegroup consisting of SiO₂, SiO, low-k dielectric materials, anddielectric materials comprising silicon and oxygen.
 7. The method ofclaim 1 wherein the mass comprises at least two layers, one of the atleast two layers comprising the dielectric material and the other of thetwo layers comprising the oxide barrier material, and wherein the secondopening is etched through both of the at least two layers.
 8. The methodof claim 1 wherein the base surface is at least partially covered bycopper oxide, silicon oxide and copper fluoride; and wherein thecleaning removes substantially all of the copper oxide, silicon oxideand copper fluoride from the base surface.
 9. The method of claim 1wherein the mixture is an aqueous mixture comprising ionic components,and wherein the ionic components consists essentially of NO₃ ⁻, F⁻ andone or more organic acid anions, at least until the cleaning.
 10. Themethod of claim 1 wherein the organic acid anion is selected from thegroup consisting of formate, acetate, propanoate, butanoate, andpentanoate.
 11. The method of claim 1 wherein the mixture comprises a pHof greater than about 1 and less than about
 4. 12. A method of cleaninga post-etch semiconductor surface comprising: providing a substratecomprising a first layer comprising a first material selected from thegroup consisting of Al₂O₃, SiO₂, SiC, silicon oxynitride andcompositions comprising silicon, carbon and hydrogen, and a second layercomprising a second material selected from the group consisting of SiO,SiO₂, and low-k dielectric materials, the first and second layers beingdisposed over a semiconductive material; forming an opening through thefirst layer and through the second layer wherein the forming comprisesetching to a third material at a base surface of the opening; exposingthe base surface to a cleaning solution formed from nitric acid,hydrofluoric acid, and one or more organic acids, at least some of theorganic acids comprising one or more carboxylic acid groups.
 13. Themethod of claim 12 wherein the etching comprises a closed barrier etch,and wherein the base surface comprises barrier material selected fromthe group consisting of a bottom anti-reflective material, a dielectricanti-reflective material, aluminum nitride and a silicon carbidematerial.
 14. The method of claim 12 wherein the exposing comprises oneor more of immersion, submersion, spraying, brush-scrubbing,spin-processing, agitation, megasonics and recirculation.
 15. The methodof claim 12 wherein the base surface comprises a copper-containingmaterial selected from the group consisting of a copper alloys, a coppercompound, and elemental copper.
 16. The method of claim 12 wherein theforming the opening further comprises etching through a materialselected from the group consisting of a bottom anti-reflective material,a dielectric anti-reflective material, aluminum nitride and a siliconcarbide material.
 17. The method of claim 12 wherein the first layer isover the second layer.
 18. The method of claim 12 wherein the secondlayer is over the first layer.